Oven control



Jne 18, 1935.

A.' P. CHESTER E'l.' AL.

OVEN CONTROL 2 Sheets-Sheet l Filed NOV. 9, 1951 ATTORNEY.;

June 18, 1935. A. P, CHESTER Er Al. 2,004,977

OVEN CONTROL Filed Nov. 9, 1931 2 Sheets-Sheet 2 INVENTORS.

60 (31 ATTORNEYs.

Patenten June 18,1935

@VEN CN'IROL Alden P. Chcster and Dewey H. Hill, Kokomo, Ind., assignorsto Globe-American Corporation,

Kokommind., a corporation Application November e, i931, serial Nq.573,748

imams.

This invention relates to an oven control for a cook stove, and moreparticularly to the type of oven control in which the cooking time isdivided into a heat supply period and la reless, cooking period. At theend of the heat supply period, the supply of fuel to the burners is shutoff and the oven vents are closed to prevent circulation of air so thatthe oven is thereby converted into a Vfireless cooker. The cooking iscompleted durin'g the reless cooking period as the oven gradually cools.In thisf type of oven control, the degree of cooking depends upon twofactors: first, thetemperature of the oven at the time the heat isturned off, and, second, the length of time required to attain thistemperature. For example, the food will be more thoroughly cooked iftwenty minutes are required to reach the desired cut-olf temperaturethan it will be if only ten minutes are required. This is true becauseordinarily cooking takes place at any temperature above 212 F. andwherea longer time is required to reach the cut-off temperature the food iskept above 212 F. for a longer time during the heat supply period.

Heretofore, in the operation of `automatic mechanism for shutting oifthe fuel supply and closing the vents, two methods have been used todetermi-ne the time of operation of the mech- 30 anism: first, athermostat/:ic method, and, second, a time-controlled method. In'the-first method the heat supply periodis automatically stopped when apredetermined temperature is reached in the'oven irrespective (of thetime required to reach that temperature. In the second method the heatsupply period is closed at a predetermined time after the start ofcooking irrespec- `tive of the temperature of the oven at that time. Inthe use of natural or artificial gas for cook- 40 ing, the pressure ofgas supplied often' varies from three to seven inches of water in asingle day, depending on the rate of use, the weather, the supply onhand and other factors. Obviously, if the thermostatic method is used;the time of the heat supply period will be much longer if the gaspressure is low than if it is high. Similarly, if the time-controlledmethod is used, the temperature f the oven at the time of shut-off willbe much less with low pressure 50 gas than with high pressure gas. Nouniformity of cooking results can, therefore, be secured merely by thesetting of a thermostat or time clock so long as an appreciablevariation in gas pressure is encountered. A pressure diierence as smallas one-half inch of water makes an immense diiference in thethoroughness with which certain foods are cooked by either of themethods discussed above.

The principal object of the present invention is to provide means bywhich the heat supply 5 period can be controlled to give a predeterminedo`ven temperature in a predetermined time. This is accomplished bydesigning the. burners to provide sufficient heat on a' relatively low@fuel pressure and then passing the fuel 10 through a pressure regulatorwhich operates to reduce the fuel pressurel to the said low pressure andmaintains said pressure irrespective of the actual pressure of fuelsupply. Thus, for a given setting of the Iburner gas valve and a givenset- 15 ting of the pressure regulator, there will always be supplied tothe burner a uniform amount of gas per unit of time. Since the heatingvalue of the gas is usually practically constant and the combustion'eicieny of a given burner 20 varies but slightly, this results in auniform rate of heat supply to the oven. The oven is preferablysurrounded by heat insulating' walls so that the-rate of heating issubstantially independent of radiation and the outside tempera- 25 ture.The uniform rate of heat. supply, therefore, insures that the oven willreach a predetermined temperature in' a predetermined time.

.When this temperature has been reached, the

heat supply is shut off land the vent is closed by either 'thethermostatic method or the timecontrolled method.v Sin'ce there is adefinite relation between the temperature and the time required to reachthat temperature, either method may be used. However, the thermostat-,ic35' y method is preferred and is illustrated herein.

Other features of the invention reside in the specic form of mechanismused for shutting olf the fuel and air supply.

Other objects and features of the invention 40 will be understood lfromthev accompanying drawings and the following description andA claims: 4

Fig. 1 is a plan view of an oven having a preferred form of controlmechanism connect'ed 45 thereto. Fig. 2 is an elevational View of thesame'in section. Fig. 3 is a detail in elevation showing the controlhandles for operating the control devices. Fig. i is an enlargedvportion of Fig. 1 showing certain parts of the control 50 apparatus inmore detail. Fig. 5 is a central sectional view in elevation 'of theparts shown in Fig. 4 and other parts associated therewith. Fig. 6 andFig. 7 are sectional views in elevation taken on the lines 6 6 and 'l-'Iof Fig. 5, re- 55 connected to any suitableI fuel supply.

spectively. Fig. 8 is a detailed view with parts removed of a particularform of thermostat which may be used with the invention.

The oven shown in the drawings consists of an outer shell I and an innershell II having a filling of heat insulating material I2 therebetweenand fitted with an oven door I3. In the lower part of the oven chamberthere is located a burner I4 supplied with fuel 'through a pipe I5leading from a valve I6. Fuel is supplied to the valve I6 by a pipe I1leading from a pressure regulator I8 in turn supplied by a pipe I9 Thepressure regulator I8 is of a common form adapted to reduce the pressureof the fuel to a relatively low pressure and to admit only so much fuelto pipe I1 as is necessary to maintain this pressure. Ihus the valve I6always receives fuel at a uniform pressure so that, with a given set--ting of valve I6, a uniform amount of fuel per unit of time isdelivered to the burner I4. The

burner, therefore, heats the oven to a predetermined degree in apredetermined length of time, as previously described.

'Ihe apparatus for automatic control of the oven vent and fuel valve isprincipally supported upon a pair of castings 20 and 2I carried upon theshell of the oven as best seen in Fig. 2; 'I'he casting 20 has formedtherein a horizontal partition 22 having openings 23 and 24. The opening24 is closed by av cover 25 andthe opening 23-is closed by a movableclosure 26. When the closure 26 is raised, the products of combustionfrom the oven follow the path indicated by the three arrows in Fig. 2,passing from the oven through the opening 23 and out through a ventopening 21 to any suitable chimney or similar disposal device. When theclosure 26 is lowered, no circulation of gases from the oven is possibleand the oven, therefore, operates as a reless cooker.

`The valve I6 is supported upon the casting 2| by means of a stud 28.'I'he said valve is of the plug-cock type having a valve plug 29 to thestem 30 of which there is fastened a radially extending pin 3| whichrests upon the top ofa stud 32 when the valve is closed, but which movesupwardly, away from the stud when the valve is opened. The valve stem 30also has attached thereto a rodK 33 extending to the front of the stoveand vcarrying at that end a pointer or handle 34. The said pointer'maybe rotated to open and close the valve I6 and registers with 'a scaleyon the front plate 35 of the stove to indicate the setting of the valve.The said scale is represented in Fig. 3 by the legend Off-lA-l/g---On. y

The casting 2I supports apair of bearing brackets 36 and 31 inthe latterof which there is clamped a bushing 38. A. tube 39 is rotatablysupported in the bearing bracket. 36 and the bushing 38 and surroundsthe lrod 33 throughout the greater part of the length of said rod. Asimilar tube 40 surrounds the remainderv ofthe rod 33 and is fastened tothe tube 39 by a semiflexible coupling 4I. The outer end of tube 40 hasfastened thereto a bushing 42 which is freely rotatable in a bearing 43carried on the front plate 35. A dial 44 is carried by said bushing andis marked with graduations visible through an opening 45 in the plate35. The bushing 42 also carries outside of the plate 35. a knob 46 bymeans of which the'tubes 39 and 40 and their associated parts may berotated.

The tube 39 has fastened thereto near the valve I6 a cam 41 carrying apin 48 positioned to engage the pin 3I. If the valve I6 is opened,therefore, it may be closed by a counter-clockwise rotation of the cam41 and it may not again be opened until said cam has been moved in aclockwise direction. After the latter movement, the pointer 34 may beturned to adjust the valve I6 as desired.

The tube 39 also carries a cam 49 having an outer surface shaped as bestshown in Fig. '7. A roller 50 is carried upon the upper end ofa slidebar 5I and engages the said surface of the cam. The slide bar isprovided with a guide slot 52 through which the tube 39 passes and whichserves to confine the movements of the bar to a verticalpath. The lowerend of the bar 5I is bent at a right angle and is fastened to the upperend of a stem 53, the lower end of which is in turn fastened to the ventclosure 26. As will be seen from Fig. '7, the shape of cam 49 is suchthat a partial revolution of the cam in a clockwise direction raises theclosure 26 to open the vent While a return to the normal position shownin that figure results in closing of the vent. y

The tube 39 also carries a collar 54 fastened thereto, which serves asan abutment for one end of a torsion spring 55, the other end of whichis fastened to the bushing 38. The spring serves tourge the tubes 39 and4D in the counterclockwise direction toward lthe position indicated inFig. 7. In that position the pin 3I rests on stud 32 and pin 48 rests onpin 3I so that no further movement of the tubes by the spring ispossible.

A thermostatic unit is provided. The said unit includes an invertedU-shaped frame 56 supported from the casting 2| by means of bolts 51.The said frame is positioned in the vent passage of the oven lbeneaththe opening 24, the cover 25 of which is removable for insertion of saidframe. Between the legs of the U-shaped frame 56 there is positioned anumber of ther-*i mostatic leaves 58 placed one above the other inparallel, spaced relation and each having each end bent about a pin 59.The pins 59 extend at both ends through openings 68 in the frame 56.'Ihe leaves 58 are made in the usual manner of two metals havingdissimilar expansion properties so yarranged as to bow downwardly whenheated. A trip rod 6I eitends vertically through suitable openings inthe leaves 58 and is provided with a toothed upper end 62 engaging teeth63 formed in the periphery of the cam 41. 'Ihe said trip rod is upwardlypressed by a spring 64 contained in a cup-shaped depression 65` in thecasting 2I and abutting against a cotter pin 66 passing through saidrod. The teeth are so shaped that the trip rod pre-4 vents turning ofthe cam 41 by the spring 55 but doesnot prevent movement thereof in theopposite direction by hand. The lower end of the trip rod carries anadjustable nut 61 positioned to be engaged by the lowermost of theleaves 58 as the said leaf is heated and bends. downwardly.` Spacerbushings 68 surround the trip 6I between the leaves 58 and each bushingserves to transmit the bending force of the leaf above to the leafbelow. In this manner, the force received by the nut 61 and rod 6I isthe total of the bending force of the several leaves. When the leaveshave bent suiilciently to press the trip rod 6I downwardlyout ofengagement with the teeth 63, the spring 55 is free to move 'cli aooe

the cams to close valve it and the vent closure et.

From Figure 7, it will be seen 'that the pe riphery oi' the cam il is ofa generally spiral form so that the trip rod @l is forced downwardly asthe cam isrotated in a clockwise di-I rection. The nut @l on the lowerend oi the trip rod is thus moved farther from engagement with thelowermost leaf 58. The leaves then must be heated to a highertemperature Ibeiore they reach the nut lil and press the trip roddownward. Thus the rotated position of the cam determines thetemperature `rwhich the trip rod is operated. The cam position forvarious temperatures is indicated by numerals on dial il!) visiblethrough the opening in the front plate of the stove.

The operation of the apparatus will novi be described. Assuming that itis desired to cook a certain food which is known. to reduire a heatsupply period of minutes and a maximum temperature of 500 at the end ofperiod. Assume also that it has been found that this temperature will bereached' in 20 minutes with the normal setting oi the pressure regulatorand with the gas valve 3A open. The knob lid is `first turned to bringthe numeral 509 into view through the opening 35, thus indicating thatthe trip rod Si has been moved downward to a point at which 500 isrequired for it to be tripped by the thermcstatic leaves 58. It will benoted that there are no teeth on the firstv9 of the cam ll and thatthis.portion of the cam has the form of an arc of a circle. No adjustment ofthe trip rod di, therefore, takes place during the iirst quarterrevolution of the cam. It Will also be seen that the entire movement ofopening the vent closure 26 takes place during the iirst quarterrevolution of the cam Q9. The pin d@ moves sumciently during thisquarter revolution to permit the gas valve to be fully opened ifnecessary. Thus the rst quarter revolution of the knob it fully opensthe vent, and arranges the parts so that the gas valve may be fullyopened. Further movement of the knob adjusts the trip rod 6l for thedesired nal temperature.

After the knob 56 has been set, the pointer 3ft is moved to the 3A markto open the gas Valve the desired amount. The gas may then be lit. Sincea constant flow of gas at a measured rate is delivered, it is certainthat the oven will then reach the desired 500 temperature in the desired20 minutes of time.

The invention claimed is:

1. In a cook stove, the combination of an oven, a burner for heatingsaid oven, a valve for controlling the supply of fuel to said burner, aspiral cam having teeth formed about its periphery, a spring tending torotate said cam in one direction, a trip member having teeth engageablewith the teeth of said cam and normally preventing rotation of said camby said spring but permitting manual rotation thereof, a thermostaticelement adapted to move when heated and engageable with said trip memberto move the same out of engagement with said cam to permit rotation ofsaid cam by'said spring, and connect-ing means between said cam andvalve for closing said valve when said cam is so rotated, the form ofsaid cam being'such that the manual rotation thereof moves the tripmember to vary its position with respect to said thermostatic elementfor varying the temperature to which the latter must be heated beforeengaging said trip member.

2. In a cook stove, the combination of an ove structure having an airvent, a closure for said vent, a burner for heating said oven, a valvetor controlling the supply of fuel to said burner, a spiral cam havingteeth formed about its periphery, a spring tending to rotate said cam inone direction, a trip member having teeth engageable with the teeth ofsaid cam and normally preventing'rotation of said cam by said spring butpermitting manual rotation thereof, a thermostatic element adapted tomove when heated and engageable with said trip member to move the sameout of engagement with said cam to permit rotation of said cam by saidspring, and connecting means between said cam, said valve and said ventclosure for closing both-said valve and vent closure when said cam is sorotated, the torm of said carri being such that the manual rotationthereof moves the trip member to vary its position vvith respect to saidthermostatic element for varying the temperature to which the lattermust be heated before engaging said trip member.

3. In a cook stove, the combination of an oven, a burner for heating thesame, a supply pipe for supplying fuel to said burner, a valve in saidsupply pipe for controlling the fiow of fuel therethrough, aheat-responsive device in said oven, mechanism connecting saidheat-responsive device and said valve and operable to close said valvewhen the temperature within the oven has reached a predeterminedmaximum, and a pressure regulator in said supply pipe located at aposition to control the pressure at said valve exclusively in suchmanner as to insure an approximately uniform predetermined fuel pressureat said burner, whereby an approximately uniform amount of heat per unitof time is supplied to said oven for a given setting of said valve andsaid pressure regulator.

4. In a cook stove, the combination of an'oven having a vent opening, aclosure for said vent opening, a burner for heating the oven, a supplypipe for'supplying fuel to said burner, a `valve in said supply pipe forcontrolling the flow of fuel therethrough, a heat-responsive device insaid oven, mechanism connecting said heat-responsive device with saidvalve and said vent closure operable to close the valve and the ventwhen the temperature Within said oven has reached a predeterminedmaximum, and a pressure regulator in said supply pipe located at aposition to control the pressure at said valve exclusively in suchmanner as to insure an approximately uniform predetermined fuel pressureat said burner, whereby an approximately uniform amount of heat per unitof time is supplied to said oven for a given4 setting of said valve andsaid pressure regulator.

ALDEN P. CHESTER. DEWEY H. HILL.

